The long range goal of this research is to determine whether deficient vagal antagonism of sympathetic nervous system (SNS) actions on the heart contributes to increased CHD risk in hostile person's. Specific aims include the use of sophisticated electrophysiologic monitoring approaches to: 1) show greater sensitivity in nonhostile young men to T-wave attenuation effects of isoproterenol infusion following vagal blockade; 2) show that vagal enhancement reduces and shortens the T-wave attenuation effects of isoproterenol infusion more in hostile young men; 3) evaluate these effects of vagal blockage and enhancement in middle-aged men and in young and middle-aged women; and 4) relate the T-wave effects in these studies to other measures of vagal tone and other biobehavioral mechanisms of cornonary-prone behavior. Four studies will be done in normal young and middle-aged men and women selected as high and low on hostility, evaluating vagal tone measures and effects of isoproterenol infusion on EKG T-wave and ST response after pretreatment with saline, neostigmine, and atropine. Demonstration that hostility is associated with deficient vagal anatagonism of SNS effects on the heart, especially in middle-aged as compared to younger persons, would suggest that diminished vagal tone is one pathway whereby high hostility contributes to increased CHD risk. Clinical studies would then be indicated to determine whether weaker vagal tone predicts increased myocardial ischemia and/or poorer outcomes in CHD patients. Knowledge gained in this research program could help to develop more effective preventive, treatment, and rehabilitation approaches to coronary disease.